A random access technique is a technique for converting a point on a time line of a digital stream to a recording position on the digital stream, and starting playback of the digital stream from the recording position. This is an essential technical basis for playing back digital streams recorded on a recording medium, such as a BD-ROM or a DVD-Video.
Digital streams are coded by a variable-length encoding method, such as MPEG2-Video or MPEG4-AVC, and the amount of information included in each frame is different. Therefore, to perform the above-described conversion for the random access, it is necessary to refer to an entry map. The entry map indicates a plurality of entry times on a time line of a digital stream in one-to-one correspondence with a plurality of entry points on the digital stream. If the time accuracy of the plurality of entry times on the entry map is one second, it is possible to efficiently perform the random access in time accuracy of one second.
For the random access targeting a video stream, it is necessary to search for an I (Intra) picture positioned at the beginning of a GOP. A data structure supporting the search for the I picture is disclosed by a prior art below:
Patent Document 1: JP Patent Application Publication No. 2000-228656.